This invention relates to water-based medical and dental cements.
Fluoroaluminosilicate glass cements (also known as xe2x80x9cglass ionomer cementsxe2x80x9d) are used extensively in restorative dentistry. Two major classes of such cements are in current use. The first class is known as conventional glass ionomers. Conventional glass ionomers typically employ as their main ingredients a homopolymer or copolymer of an xcex1,xcex2-unsaturated carboxylic acid (e.g., poly acrylic acid, copoly (acrylic, itaconic acid), etc.), a fluoroaluminosilicate (xe2x80x9cFASxe2x80x9d) glass, water, and chelating agent such as tartaric acid. Conventional glass ionomers typically are supplied in powder/liquid formulations that are mixed just before use. The mixture will undergo self-hardening in the dark due to an ionic reaction between the acidic repeating units of the polycarboxylic acid and cations leached from the glass.
The second major class of glass ionomer cements is known as resin-modified glass ionomer (xe2x80x9cRMGIxe2x80x9d) cements. Like a conventional glass ionomer, an RMGI cement employs an FAS glass. However, the organic portion of an RMGI is different. In one type of RMGI, the polycarboxylic acid is modified to replace or end-cap some of acidic repeating units with pendent curable groups and a photoinitiator is added to provide a second cure mechanism, e.g., as in U.S. Pat. No. 5,130,347. Acrylate or methacrylate groups are usually employed as the pendant curable group. A redox cure system can be added to provide a third cure mechanism, e.g., as in U.S. Pat. No. 5,154,762. In another type of RMGI, the cement includes a polycarboxylic acid, an acrylate or methacrylate-functional monomer and a photoinitiator, e.g., as in Mathis et al., xe2x80x9cProperties of a New Glass Ionomer/Composite Resin Hybrid Restorativexe2x80x9d, Abstract No. 51, J. Dent Res., 66:113 (1987) and as in U.S. Pat. Nos. 5,063,257, 5,520,725, 5,859,089 and 5,962,550. Photoinitiator cure systems have been said to be preferred (see, e.g., U.S. Pat. Nos. 5,063,257 and 5,859,089). Conventional peroxide oxidation agents have been noted to be unstable in ionomer cements (see, e.g., U.S. Pat. No. 5,520,725). Some patents exemplify RMGI cements that include a polycarboxylic acid, an acrylate or methacrylate-functional monomer and a redox or other chemical cure system (see, e.g., U.S. Pat. Nos. 5,520,725 and 5,871,360). Various monomer-containing or resin-containing cements are also shown in U.S. Pat. Nos. 4,872,936, 5,227,413, 5,367,002 and 5,965,632. RMGI cements are usually formulated as powder/liquid or paste/paste systems, and contain water as mixed and applied. They harden in the dark due to the ionic reaction between the acidic repeating units of the polycarboxylic acid and cations leached from the glass, and commercial RMGI products typically also cure on exposure of the cement to light from a dental curing lamp.
There are many important benefits of using glass ionomer cements. Fluoride release from glass ionomers tends to be higher than from other classes of cements such as metal oxide cements, compomer cements (anhydrous light-curable single-part paste systems containing FAS glass, as shown in Published PCT Application No. WO 97/18792 and U.S. Pat. Nos. 5,859,089, 5,962,550 and 6,126,922) or fluoridated composites, and thus glass ionomer cements are associated with cariostatic behavior. Although differences exist between commercial brands of glass ionomer cements, in general it is believed that high fluoride release leads to better cariostatic protection. Another important reason for using glass ionomer cements is the very good clinical adhesion of such cements to tooth structure, thus providing highly retentive restorations. Because conventional glass ionomers do not need an external curing initiation mode, they can be placed in bulk as a filling material in deep restorations, without requiring layering. However, conventional glass ionomers are rather technique sensitive (e.g., the performance can depend on the mixture ratio and the manner and thoroughness of mixing) and are quite brittle as evidenced by their low flexural strength. Thus restorations made from conventional glass ionomer cement mixtures tend to undergo fracture quite readily. Cured RMGIs have increased flexural strength and are less prone to mechanical fracture than conventional glass ionomer cements.
Photocurable RMGIs typically are placed in layers to overcome the light attenuation that accompanies increased thickness. This attenuation can be offset somewhat by instead or in addition employing a dark-curing chemical cure mechanism (such as the three-way cure mechanism shown in the above-mentioned U.S. Pat. No. 5,154,762 or the two-way or three-way cure mechanisms shown in the above-mentioned U.S. Pat. Nos. 5,520,725 and 5,871,360). However, for highly viscous RMGI cement mixtures it usually is necessary to perform a preliminary tooth priming or conditioning step in which a low viscosity aqueous-organic conditioner or primer is applied to the tooth prior to placement of the RMGI mix. Thus an additional step is required to obtain a clinically desirable restoration.
Neither conventional glass ionomers nor RMGIs have entirely satisfactory properties, and further improvements in the performance and ease of use of glass ionomer cements would be desirable.
The present invention provides, in one aspect, a glass ionomer cement comprising a mixture of a polymer having a plurality of acidic repeating units but being substantially free of polymerizable vinyl groups (xe2x80x9cPolymer Axe2x80x9d) and a polymer having a plurality of acidic repeating units and a plurality of polymerizable vinyl groups (xe2x80x9cPolymer Bxe2x80x9d). Preferably the cements of the invention comprise:
a) Polymer A;
b) Polymer B;
c) FAS glass;
d) redox cure system that can initiate dark cure of the vinyl groups; and
e) water.
The invention also provides methods for making and using glass ionomer cements.
Preferred embodiments of the cements of the invention can be used without requiring a preliminary tooth priming or conditioning step and without requiring a curing lamp. The cements offer ease of mixing, convenient viscosity, convenient cure, good flexural strength, good adhesion to dentin and enamel, and high fluoride release, even when cured in thick sections and in the dark.